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Magnetic balls

  1. Sep 16, 2014 #1
    Is it possible to create a ball with a positive magnetic core and a negative exterior? And vice versa?
     
  2. jcsd
  3. Sep 16, 2014 #2
    First of all, you're using the wrong terminology. Magnets don't have negative or positive charges, they have north and south poles, that's very different from electric charges. You can have a positively or negatively charged particle but you can't have a north pole without having the south pole on the same object, in other words you can't have a magnetic monopole, if you break up a bar magnet into peaces every single one of them will have north and south poles. Field lines of magnetic field should be closed curves because otherwise it would violate Gauss's law for magnetism (which states that divergence of magnetic vector field is zero).

    I think it's impossible to create a perfectly shaped sphere with magnetic field lines uniformly pointing outwards everywhere on its surface.
     
  4. Sep 16, 2014 #3
    What about this? http://www.eachmall.com/goods-23297...hoOv0Dfuh893JhJwV2ymMCQmOEaLwtGKyIhoCnofw_wcB
     
  5. Sep 16, 2014 #4

    berkeman

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  6. Sep 16, 2014 #5
    How would all of the balls stick together? Wouldn't they repel?
     
  7. Sep 16, 2014 #6

    berkeman

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    I suppose they might have 3 sets of N/S poles for each ball. Picture a rectangular 3-D coordinate system with the origin at the center of the ball. Then magnetize the ball with N pointing out the + end of each x, y, z axis, and S pointing out the - end of each axis.

    If you visit a hobby store and experiment with a set of magnetic balls a bit, you can probably figure out how they are magnetized...
     
  8. Sep 17, 2014 #7
    If you took two small balls in your hand and rotated them around, I'm sure you'll find that they don't stick in every direction.

    If you somehow made a ball with a positive magnetic core and a negative outer layer (by assembling a million small bar magnets, all facing inward), then the field outside the ball would be zero, and you might as well not have a magnet at all. This is because of Gauss's law, applied to a magnetic "charge".
     
  9. Sep 18, 2014 #8

    CWatters

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    No. From the outside this would look like an isolated magnetic monopole which aren't thought to exist..

    http://en.m.wikipedia.org/wiki/Magnetic_monopole
     
  10. Sep 18, 2014 #9

    Vanadium 50

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    Actually, if you built one of these - perhaps by sticking a lot of bar magnets radially in Play-Doh - you will find from the outside there is little to no field. Try it!
     
  11. Sep 18, 2014 #10
    is that what hes doing here?
     
    Last edited by a moderator: Sep 25, 2014
  12. Sep 19, 2014 #11

    CWatters

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    He's certainly NOT creating a "monopole magnet".
     
    Last edited by a moderator: Sep 25, 2014
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